Block copolymer micelle composition having an enhanced drug-loading capacity and sustained release

ABSTRACT

The present invention relates to a micelle drug composition having an enhanced drug-loading capacity and improved sustained-release characteristics. The composition comprises an amphilphilic block copolymer wherein at least one hydrophilic blocks and at least one hydrophobic blocks form shell and core, respectively, said hydrophobic block comprises 1.1 to 30 functional groups selected from the group consisting of carboxyl, amine, hydroxyl, amide, thiol and sulfonic acid groups, in a hydrophobic block chain of the copolymer.

FIELD OF THE INVENTION

The present invention relates to a micelle drug composition having anenhanced drug-loading capacity and improved sustained drug-releasecharacteristics.

BACKGROUND OF THE INVENTION

Amphiphilic block copolymers that can form a core-shell type micelle inan aqueous medium have been used for delivering hydrophobic drugs suchas anti-cancer drugs, adriamycin and paclitaxel, the drug being loadedin the hydrophobic core and the hydrophilic shell enhancing thesolubilization of the micelle.

Such a micelle having a size of not more than 200 nm and apolyethyleneoxide hydrophilic shell is neither easily destroyed by thereticuloenthelial or monomuclear phagocyte system nor excreted throughkidney, and therefore, circulates in a living body for a long period oftime, accumulating at the blood vessel around tumors where the transferof materials is much enhanced and more selective than that around normalcells.

The hydrophobic block of such amphiphilic block copolymers may bedivided into two groups, i.e., (i) a hydrophobic block having nofunctional group, e.g. polylactide, polycarprolactone,poly(lactide-glycolide), poly(β-benzyl L-aspartate), as way disclosed inKorean Patent Publication Nos. 1999-69033 and 2001-105439, EuropeanPatent Publication No. 583055, U.S. Pat. No. 6,322,805 and JapanesePatent Publication No. 1994-206815, and (ii) a hydrophobic block havinga plurality of functional groups, e.g., poly(β-substituted aspartate),poly(γ-substituted glutamate), poly(L-leucine), described in EuropeanPatent Publication No. 583955. In case the hydrophobic block has nofunctional group, the drug loading capacity of the hydrophobic core islimited, whereas when contains too much functional groups, for example,300 or more per hydrophobic block, the amphiphilic nature of thecopolymer is lost and dissolves in an aqueous medium and cannot form amicelle. Therefore, the step of chemically bonding a hydrophobic drug tosuch copolymer has been performed to prepare a delivery composition.

Accordingly, in order to solve this problem and increase the drugloading capacity and sustained-release characteristics of micelle drugcomposition, there has been a need to develop amphiphilic blockcopolymeric micelles containing a small quantity of functional groups ina hydrophobic block.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to providea micelle composition for drug delivery having an enhanced drug-loadingcapacity and sustained-release characteristics.

And it is another object of the present invention to provide a method ofpreparing such micelle composition, characterized by employing afunctional monomer.

Further, it is a further object of the present invention to provide apharmaceutical composition containing a hydrophobic drug in thehydrophobic core of the micelle composition.

DETAILED DESCRIPTION OF THE INVENTION

The amphiphilic block copolymer of the present invention comprises oneor more of hydrophilic blocks(A) and hydrophobic blocks(B), which formsa micelle in an aqueous medium, the hydrophilic block(A) and thehydrophobic block(B) forming a shell and a core, respectively. Ahydrophobic drug becomes water-soluble when the drug is introduced intothe hydrophobic core of such micelle. The hydrophobic block(B) of thepresent invention carries 1.1 to 30 functional groups, preferably 2 to30 functional groups, selected from the group consisting of carboxyl,amine, hydroxyl, amide, thiol and sulfonic acid groups which enhance thecore's affinity to the drug. Preferably, the amount of the amphiphilicblock copolymer having such functional groups is in the range of 0.1 to10% by weight, based on the total weight of the micelle composition.

The hydrophilic block of the amphiphilic block copolymer has a molecularweight of preferably 100 to 30,000 Da, more preferably, 1,000 to 12,000Da. The hydrophilic block of the copolymer may be a poly(alkylene oxide)or monoalkoxy poly(ethylene oxide) block, preferably, poly(ethyleneoxide) or methoxy poly(ethylene oxide) block.

The hydrophobic block of the amphiphilic block copolymer is preferablybiodegradable and biocompatible, and the molecular weight of thehydrophobic block is preferably from 200 to 30,000 Da, more preferably,from 1,000 to 15,000 Da. The hydrophobic block may be a polylactide,polycaprolactone, polyglycolide, copolymer of lactide and glycolide,polyorthoester, polyanhydride, polyphosphazine, poly amino acid, amixture thereof, or a derivative thereof, preferably, a polylactide or acopolymer of lactide and glycolide.

The functional group may be a carboxyl, amine, hydroxyl, amide, thiol orsulfonic acid group. An optimal number of the functional groupintroduced to the hydrophobic block is 1.1 to 30, which enhances themicelle core's interaction with an essentially water-insoluble drugwhile maintaining a micellar form in an aqueous medium. Further, suchaffinity of the drug to the hydrophobic core brings out a desirablesustained-release characteristics of the drug.

Further, the amount of functional groups introduced controls thedegradation rate of the micelle of the present invention. Preferably,the present invention employs a poly(ethylene oxide) as the hydrophilicblock, and a polylactide or polycaprolactone as the hydrophilic block,which are nontoxic and have desired biodegradability andbiocompatibility.

The amphiphilic block polymer of the present invention may be a diblockpolymer of the hydrophilic block(A)-hydrophobic block(B) type, or atriblock polymer of the hydrophobic block(B)-hydrophilicblock(A)-hydrophobic block(B) or hydrophilic block(A)-hydrophobicblock(B)-hydrophilic block(A) copolymer type.

As one embodiment of the present invention, the amphiphilic block offormula (I) comprises a hydrophobic block containing a carefullycontrolled amount of functional groups:

wherein R₁ is H, C₁₋₄ alkyl or C₁₋₄ acyl;

R₂ is H, C₁₋₉ alkyl, aryl or C₁₋₉ arylalkyl;

x is a number ranging from 10 to 400;

y is a number ranging from 10 to 300;

z is a number ranging from 1.1 to 30; and

W is selected from the group consisting of carboxyl, amine, hydroxyl,amide, thiol and sulfonic acid groups.

Herein, x, y or z represent the average number of repeating units of thepolymer.

Preferably, the amphiphilic block of formula (I) comprises a hydrophobicblock wherein W is a carboxyl group. Preferably, z is the number rangingfrom 2 to 30. The amphiphilic block of formula (I) comprises ahydrophobic block wherein a ratio z/y preferably ranges from 0.015 to 2,more preferably from 0.02 to 1.5.

The amphiphilic block copolymer of the present invention may be preparedby introducing a controlled amount of functional groups into thehydrophobic block(B) to enhance the core's affinity to a hydrophobicdrug.

As one embodiment of the present invention, the amphiphilic blockcopolymer of formula (I) is prepared as follows:

In the presence of a polyethyleneoxide or monomethoxypolyethyleneoxide,a heterocyclic ester of D,L-lactide is reacted with3-{(bezyloxycarbonyl)methyl}-1,4-dioxane-2,5-dione (BMD, a functionalmonomer), to obtain an amphilphilic block copolymer, the hydrophobicblock thereof comprising benzyl groups, followed by hydro-debenzylationunder hydrogen in the presence of a catalyst to obtain an amphiphilicblock copolymer comprising carboxyl groups (see International Journal ofBiological Macromolecules, 1999, 25, 265).

The functional monomer,3-{(bezyloxycarbonyl)methyl}-1,4-dioxane-2,5-dione (BMD), may beprepared by benzylation of the carboxyl group of aspartic acid in thepresence of an acid catalyst and then replacing the amine group with ahydroxyl group. Then, the resultant is bromoacetylated in the presenceof a base catalyst to obtain the cyclic structure of BMD (seeMacromolecules, 1988, 21, 3338).

In accordance with one aspect of the present invention, there isprovided a pharmaceutical micellar composition having a core-shellstructure, the hydrophobic core of the micelle being designed to load ahydrophobic drug to a higher capacity.

The micellar composition and a drug are dissolved in an organic solvent,and then, the organic solvent is replaced with water, e.g., by dialysis,to obtain an aqueous micelle solution containing the drug. Then, thesolution is lyophilized, sterilized and sealed to obtain apharmaceutical micelle composition containing the drug.

The drug may be present in an amount ranging from 0.1 to 5% by weightbased on the total weight of the pharmaceutical composition. A drughaving a solubility of not more than 10 mg/ml may be employed. The drugmay be an anti-cancer drug, antiflammation, sex hormone, steroid,anti-hypertensive drug or anti-emesis drug. Preferably, the drug may bepaclitaxel, camptothecin, biphenyl dimethyl dicarboxylate, piposulfan,danazole, taxotere, adriamycin, indomethacin, etoposide, itraconazole,nystatin, hemoglobin or omeprazole.

One embodiment of the medicinal composition of the present invention canbe prepared as follows:

10 to 500 mg of the amphiphilic block copolymer of formula I and 2 to200 mg of a drug, e.g. paclitaxel, adriamycin or indomethacin, aredissolved in 2 to 50 ml of an organic solvent, e.g. tetrahydrofuran ordimethylformamide, and 10 to 100 ml of distilled water is added thereto.Then, the mixture is stirred for 12 to 36 hours and dialyzed to obtainan aqueous micelle solution containing the drug in the hydrophobic coreof the micelle. The aqueous micelle solution may be lyophilized,sterilized and sealed to obtain a pharmaceutical composition forinjection.

The micelle composition may be administrated orally or parenterally, forexample by injection, for example at a drug concentration of 0.01 to 5mg/ml.

The micelle composition of the present invention has a markedlyincreased drug loading capacity, and sustained-drug releasecharacteristics.

The present invention is further described in the following Exampleswhich are given only for the purpose of illustration, and are notintended to limit the scope of the invention.

Preparation of the Amphiphilic Block Copolymers

PREPARATION EXAMPLE 1

A mixture of 4.0 g of methoxy poly(ethylene oxide) (M.W.=5000), 5.7 g ofD,L-lactide recrystallized from ethyl acetate, 0.3 g of3-{(bezyloxycarbonyl)methyl}-1,4-dioxane-2,5-dione (BMD, a functionalmonomer), and 40 mg of stannous octoate (a catalyst) was placed in around-bottomed flask and evauated for 30 min. to achieve a pressure of0.001 mmHg. Then, the mixture was allowed to polymerize at 168° C. for 2hours to obtain a diblock copolymer of poly(ethylene oxide-b-lactide),the benzyl groups being introduced into the polylactide block. 4 g ofthe resultant block copolymer was dissolved 125 ml of dioxane in anErlenmeyer flask, and 1 g of a Pt/C catalyst was added thereto. Theflask was filled with hydrogen, and then the mixture was allowed toundergo hydro-debenzylation at room temperature, to obtain a diblockcopolymer of poly(ethylene oxide-b-lactide), having carboxyl groupsintroduced into the polylactide block. Nuclear magnetic resonance(NMR)spectroscopy was performed to determine the values of x, y and z fromthe intensity of each peak of NMR, respectively. The structure of theblock copolymer is shown below:

wherein R₁ is CH₃; R₂is H ; x=113; y=55.7; z=1.34; and z/y=0.0241.

PREPARATION EXAMPLE 2

A poly(ethylene oxide-b-lactide) diblock copolymer was prepared byrepeating the procedure of Preparation Example 1, except for employing4.0 g of methoxy poly(ethylene oxide)(M.W.=5000), 5.4 g of D,L-lactiderecrystallized from ethyl acetate, and 0.6 g of BMD. The structure ofthe block copolymer is the same as a preparation Example 1, except forx=113; y=49.4; z=2.78; and z/y=0.0563.

PREPARATION EXAMPLE 3

A poly(ethylene oxide-b-lactide) diblock copolymer was prepared byrepeating the procedure of Preparation Example 1, except for employing4.0 g of methoxy poly(ethylene oxide)(M.W.=5000), 5.1 g of D,L-lactiderecrystallized from ethyl acetate, and 0.9 g of BMD. The structure ofthe block copolymer is the same as a preparation Example 1, except forx=113; y=38.2; z=3.74; and z/y=0.0979.

PREPARATION EXAMPLE 4

A poly(ethylene oxide-b-lactide) diblock copolymer was prepared byrepeating the procedure of Preparation Example 1, except for employing4.0 g of methoxy poly(ethylene oxide)(M.W.=5000), 4.0 g of D,L-lactiderecrystallized from ethyl acetate, and 2.0 g of BMD. The structure ofthe block copolymer is the same as a preparation Example 1, except forx=113; y=33.3; z=11.5; and z/y=0.345.

PREPARATION EXAMPLE 5

A poly(ethylene oxide-b-lactide) diblock copolymer was prepared byrepeating the procedure of Preparation Example 1, except for employing4.0 g of methoxy poly(ethylene oxide)(M.W.=5000), 2.0 g of D,L-lactiderecrystallized from ethyl acetate, and 4.0 g of BMD as the functionalmonomer. The structure of the block copolymer is the same as apreparation Example 1, except for x=113; y=16.7; z=23.0; and z/y=1.38.

COMPARATIVE PREPARATION EXAMPLE 1

A poly(ethyleneoxide-b-lactide) diblock copolymer was prepared byrepeating the procedure of Preparation Example 1, except for employing4.0 g of methoxy poly(ethylene oxide)(M.W.=5000) and 6.0 g ofD,L-lactide recrystallized from ethyl acetate, without adding BMD. Thestructure of the block copolymer is the same as a preparation Example 1,except for x=113; y=56.1; z=0; and z/y=0

COMPARATIVE PREPARATION EXAMPLE 2

A poly(ethylene oxide-b-lactide) diblock copolymer was prepared byrepeating the procedure of Preparation Example 1, except for employing4.0 g of methoxy poly(ethylene oxide)(M.W.=5000) and 6.0 g of BMD,without adding D,L-lactide. The structure of the block copolymer is thesame as a preparation Example 1, except for x=113; y=0; and z=30.3.

Physicochemical Properties of the Diblock Copolymers

Physicochemical properties of the amphiphilic copoymers prepared inPreparation Examples 1 to 5 and Comparative Examples 1 and 2 wereevaluated. Nuclear magnetic resonance spectroscopy and gel permeationchromatography were used to determine the poly(ethylene oxide)(PEO)/polylactide (PLA) weight ratio and the molecular weight,respectively (see Table 1). TABLE 1 M.W. Weight ratio Distri- (wt %)bution y z z/y (PEO/PLA) M.W. (PDI) Preparation 55.7 1.34 0.024154.1/45.9 10000 1.14 Example 1 Preparation 49.4 2.78 0.0563 55.3/44.79010 1.14 Example 2 Preparation 38.2 3.74 0.0979 59.5/40.5 8480 1.14Example 3 Preparation 33.3 11.5 0.345 53.2/46.8 10500 1.13 Example 4Preparation 16.7 23.0 1.38 49.0/51.0 10200 1.13 Example 5 Comparative56.1 0 0 55.3/44.7 10500 1.13 Preparation Example 1 Comparative 0 30.3 —48.7/51.3 10700 1.14 Preparation Example 2Preparation of the Medicinal Agent Compositions

EXAMPLES 1 to 5

100 mg of each copolymer prepared in Preparation Examples 1 to 5, and 50mg of paclitaxel were dissolved in 10 ml of dimethylformamide. Then, 10ml of distilled water was added thereto and the mixture was stirred for24 hours. The resultant mixture was put into a dialysis bag and placedin distilled water for 24 hours to obtain a pharmaceutical compositioncontaining paclitaxel.

COMPARATIVE EXAMPLES 1 and 2

Pharmaceutical compositions containing paclitaxel were prepared by usingthe copolymers prepared in Comparative Preparation Examples 1 and 2,respectively, by the same method of Example 1.

Physical Properties of the Medicinal Agent Compositions

The drug release rate of each of the compositions prepared in Examples 1to 5 and Comparative Examples 1 and 2 was measured according to theprocedure described in the 2nd volume of Korea Pharmacopeia.

Each micelle containing paclitaxel was homogenously dissolved in 10 mlof a dissolution solution(phosphate buffer, pH 7.4), and then theresultant solution was dialyzed by using a dialysis membrane(molecularweight cutoff, MWCO=8,000). Every hour, 1 ml of the drug solutionreleased through the membrane was taken and 1 ml of the phosphate bufferwas added thereto. Then, the resultant solution was diluted with 2 ml ofacetonitrile, and quantified by HPLC to determine the drug release rate.

Table 2 shows the micelle diameter, the saturation drug content, thedrug release time and the degradation time of the micelle containingpaclitaxel. The micelle diameter and the saturation drug content weremeasured by dynamic light scattering and UV spectrometer, respectively.The drug release time is defined by the time required for releasing 50%of the drug. TABLE 2 Micelle Saturation drug Drug Degradation diametercontent release time time of the (nm) (wt %) (hr) micelle (day) Example1 30.0 8.0 21 10 Example 2 28.0 13.7 40 7 Example 3 34.8 14.9 52 6Example 4 31.3 16.9 59 5 Example 5 28.5 16.8 60 4 Comparative 42.8 3.8 820 Example 1 Comparative — — — — Example 2

As can be seen from Tables 1 and 2, the micelles of Examples 1 to 5 havea diameter of about 30 nm, which is appropriate for an injectable drugdelivery system.

Each of the compositions of Examples 1 to 5 contained a higher amount ofthe drug in the hydrophobic core than that of Comparative Example 1. Forexample, the saturation drug content of the composition of Example 3(z=3.74, z/y=0.0979) was approximately 4-fold higher than that ofComparative Example 1 (z=0).

With more carboxyl groups introduced into the hydrophobic block, thedrug release time becomes longer. Therefore, by controlling the amountof carboxyl group introduced, one can adjust the sustained-releasecharacteristics of the composition. Further, with increasing the numberof carboxyl groups introduced, the micelle degradation time becomesshorter. Accordingly, a micelle composition having more carboxyl groupswill rapidly degrade after releasing the drug.

However, if the block copolymer contained too much carboxyl groups(z>30), it fails to form a micelle (see Comparative Example 2 of Table2), and thus, such copolymer is not suitable for drug delivery system.

It can be seen from the above results, when from 1.1 to 30 carboxylgroups are introduced into the hydrophobic block of the amphilphiliccopolymer, the micelle therefrom can carry a large amount of ahydrophobic drug, and exhibit sustained-release characteristics.

While the embodiments of the subject invention have been described andillustrated, it is obvious that various changes and modifications can bemade therein without departing from the spirit of the present inventionwhich should be limited only by the scope of the appended claims.

1. A micelle composition for drug delivery system comprising anamphilphilic block copolymer having at least one hydrophilic blocks(A)and at least one hydrophobic blocks(B), the hydrophobic block carrying1.1 to 30 functional groups selected from the group consisting ofcarboxyl, amine, hydroxyl, amide, thiol and sulfonic acid groups, in ahydrophobic block chain of the copolymer.
 2. The composition of claim 1,wherein the amphiphilic block copolymer is present in an amount rangingfrom 0.1 to 10% by weight, based on a total weight of the micellecomposition.
 3. The composition of claim 1, wherein a molecular weightof the hydrophilic block is 100 to 30,000 Da.
 4. The composition ofclaim 3, wherein the hydrophilic block(A) is polyethyleneoxide ormethoxypolyethyleneoxide.
 5. The composition of claim 1, wherein amolecular weight of the hydrophobic block(B) is 200 to 30,000 Da.
 6. Thecomposition of claim 1, wherein the amphiphilic block copolymer is adiblock polymer of the hydrophilic block(A)-hydrophobic block(B) type,or a triblock polymer of the hydrophobic block(B)-hydrophilicblock(A)-hydrophobic block(B) or hydrophilic block(A)-hydrophobicblock(B)-hydrophilic block(A) type.
 7. The composition of claim 1,wherein the hydrophobic block is selected from the group consisting ofpolylactide, polycaprolactone, polyglycolide, a copolymer of lactide andglycolide, polyorthoester, polyanhydride, polyphosphazine, poly aminoacid, a mixture thereof, and a derivative thereof.
 8. The composition ofclaim 1, wherein the amphiphilic block copolymer is represented byformula (I):

wherein R, is H, C₁₋₄ alkyl or C₁₋₄ acyl; R₂ is H, C₁₋₉ alkyl, aryl orC₁₋₉ arylalkyl; x is a number ranging from 10 to 400; y is a numberranging from 10 to 300; z is a number ranging from 1.1 to 30; and W isselected from the group consisting of carboxyl, amine, hydroxyl, amide,thiol and sulfonic acid groups.
 9. The composition of claim 8, wherein Wis a carboxyl group.
 10. The composition of claim 8, wherein a ratio z/yranges from 0.015 to
 2. 11. The composition of claim 10, wherein theratio z/y ranges from 0.02 to 1.5.
 12. A pharmaceutical compositioncomprising a hydrophobic drug introduced in the hydrophobic block(B) ofthe micelle composition according to any one of claims 1 to
 11. 13. Thecomposition of claim 12, wherein the drug is selected from the groupconsisting of paclitaxel, camptothecin, biphenyl dimethyl dicarboxylate,piposulfan, danazole, taxotere, adriamycin, indomethacin, etoposide,itraconazole, nystatin, hemoglobin and omeprazole.
 14. The compositionof claim 12, wherein the drug is present in an amount ranging from 0.1to 5% by weight, based on the total weight of the micelle composition.